Quality Control in Galvanized Steel Coil Production

1. What Is Galvanized Steel Coil?

Galvanized steel coil is steel coated with an aluminum-zinc alloy and supplied in large, round coils. The coating acts as armor, protecting the steel from corrosion and rust caused by the environment. This improves durability and makes the coil useful for industrial and consumer products such as steel pipes, purlins, machinery, equipment, and factories.

2. Advantages of Galvanized Steel Coil

In addition to strong protection, galvanized steel coil offers many notable advantages:

• Smooth, glossy surface: A protective chemical treatment keeps the steel surface bright and attractive, and makes cleaning easier.
• High corrosion resistance: The zinc coating improves corrosion resistance and protects the steel core outdoors and in chemical environments.
• Modern manufacturing technology: The product uses zinc imported from Korea and Australia, surface-treatment chemicals from India, and steel substrate produced domestically or imported from Korea, Japan, China, Brazil, and Australia.
• Impact-resistant and durable: A thick Z12–Z27 zinc coating improves load resistance and protects the inner steel from mechanical and environmental damage. With proper use, the product can last up to 50 years without maintenance.

These advantages make galvanized steel coil essential in many industries and fields.

3. Applications of Galvanized Steel Coil

Manufacturers slit, cut, or process the steel coil into products for many industries, including:

• Residential and commercial construction: Steel pipes, corrugated roofing, prefabricated steel buildings, partitions, ceiling frames, and more.
• Household appliances:Refrigerators, televisions, washing machines, water heaters, air conditioners, computers, ventilation and heating systems, and more.
• Mechanical engineering: Automotive manufacturing, shipbuilding, containers, and more.
• Construction:Building materials for factories, plants, hospitals, warehouses, schools, and theaters, as well as advertising panels and signs.
• Manufacturing of processed goods and handicrafts
• Galvanized steel coil is used to make steel pipes, roofing sheets, and steel boxes.

4. Galvanized Steel Coil Manufacturing Process

• Step 1: Pickling and surface cleaning. Hot-rolled steel coil is pickled to remove dirt, rust, and other contaminants so the zinc coating can adhere as fully as possible.
• Step 2: Cold rolling to the required thickness. Cold rolling at low temperatures increases hardness, tensile strength, and resistance to deformation.
• Step 3: Annealing.The steel strip enters a NOF (Non-Oxidising Furnace) annealing furnace to reach the required temperature before galvanizing. Its hardness is also adjusted to meet technical requirements.
• Step 4: Galvanizing. The steel strip enters a bath whose main component is zinc. An electric current causes zinc ions to adhere to the strip surface, forming the required coating.
• Step 5: Surface passivation. The steel strip leaves the bath, dries, and undergoes passivation to form the galvanized strip.
• Step 6: Exit accumulation
• Step 7: Recoiling

5. Quality Control for Galvanized Steel Coil:

Hardness and coating composition are two key quality criteria for galvanized steel coil.

1. Hardness of Galvanized Steel Coil:

- Before galvanizing, the steel strip passes through a NOF (Non-Oxidising Furnace) annealing furnace. Annealing changes the coil hardness, which is adjusted up or down according to technical requirements. The annealing process must be controlled to prevent excessive deviation from the required hardness.

If the strip is too hard, it becomes brittle and may crack or break during forming and processing.

If the strip is too soft, the finished product may have low strength and deform or dent during use and processing.

Therefore, hardness testing after galvanizing is necessary to ensure the finished product has the required mechanical properties.

** SOLUTION:

Portable Rockwell Hardness Tester

Designed for plants producing galvanized steel coil, galvanized sheet, galvanized steel pipes, and more.

Model: AFFRI MK II – Hardtest II

Origin:Italy

Applications:Measures strip hardness after slitting and before pipe forming.

Complies with DIN 50157 / ASTM B-724 / ASTM E-110.

Advantages:

• Measures on the production line in seconds without cutting a sample; can test steel sheets as thin as 0.06 mm.
• Checks pipe hardness before forming and welding.
• Saves time without interrupting production.
• LCD displays two hardness scales at once (HRB–HV, HV–N/mm², HRB–HB, etc.).

2. Composition of the Zinc Coating:

The plating bath is primarily zinc (Zn), over 99%, with trace amounts of elements such as aluminum (Al), iron (Fe), copper (Cu), and antimony (Sb).

Each element affects the coating’s mechanical properties. Trace-element composition varies according to each manufacturer’s requirements.

Therefore, identifying the elements in the plating bath is essential for optimizing cost and coating quality, since the coating directly determines product quality.

**SOLUTION: OES spectrometer for alloy composition analysis.

An alloy OES spectrometer for laboratories with high accuracy and a wide analytical wavelength range: 116–766 nm (elements H–U).

Model: Hitachi High-Tech – OE750

Origin:Germany

Applications:Analyzes the composition of zinc alloys in the plating bath.

Advantages:

• Direct optical path (no fiber-optic cable) ensures excellent light transmission.
• High-resolution Multi-CMOS optics with 16 sensors.
• Low detection limits for selected elements: C 5 ppm; B 1 ppm; Si 5 ppm; P 2 ppm; S 5 ppm; Mg 1 ppm; N 10 ppm; H 100 ppm, etc.
• The GRADE database includes more than 350,000 alloy grades and over 15 million names from 70 countries, covering standards such as DIN/EN, ASTM, AISI, JIS, and GOST.

For consultation or a demo: Phone/Zalo (24/7), Chan Huy – 0902.903.826